The larvae of the black soldier fly (BSFL, Hermetia illucens) efficiently close resource cycles. Next to the nutrient-rich insect biomass used as animal feed, the residues from the process are promising plant fertilizers. Besides a high nutrient content, the residues contain a diverse microbial community and application to soil can potentially promote soil fertility and agricultural production through the introduction of beneficial microbes. This research assessed the application of the residues on plant-associated bacterial and fungal communities in the rhizosphere of a grass-clover mix in a 42-day greenhouse pot study. Potted soil was amended with BSFL residues (BR+) or conventional compost (CC+) produced by Rwandan waste management companies in parallel to residues and compost sterilized (BR-, CC-) by high-energy electron beam (HEEB) as abiotic controls. The fertilizers were applied at a rate of 150  kg N  ha−1. Soil bacterial and fungal communities in both fertilizer and soil were assessed by high-throughput sequencing of ribosomal markers at different times after fertilizer application. Additionally, indicators for soil fertility such as basal respiration, plant yield and soil physicochemical properties were analyzed. Results showed that the application of BSFL residues influenced the soil microbial communities, and especially fungi, stronger than CC fertilizers. These effects on the microbial community structure could partly be attributed to a potential introduction of microbes to the soil by BSFL residues (e.g., members of genus Bacillus) since untreated and sterilized BSFL residues promoted different microbial communities. With respect to the abiotic effects, we emphasize a potential driving role of particular classes of organic matter like fiber and chitin. Indeed, especially taxa associated with decomposition of organic matter (e.g., members of the fungal genus Mortierella) were promoted by the application of BSFL residues. Soil fertility with respect to plant yield (+17% increase compared to unamended control) and basal respiration (+16% increase compared to unamended control) tended to be improved with the addition of BSFL residues. Findings underline the versatile opportunities for soil fertility arising from the application of BSFL residues in plant production and point to further research on quantification of the described effects.

The disposal of feacal matter from Urine Diversion Dry Toilets is a significant challenge due to limited land availability, possible underground water contamination, and the risk of spreading diseases. The collected faecal matter can be fed to Black Soldier Fly Larvae to produce protein-rich larvae used as animal feed. The disposal of the leftover waste (BSFL residue) is still a problem due to the risk of residual pathogen contamination. The BSFL residue contains residual plant nutrients and can be further processed into biochar. Faecal matter biochar offers an exciting value proposition where the pyrolysis process guarantees a 100% pathogen elimination. It also results in significant waste reduction in transport, storage weight, and volume. A preliminary study was conducted to (i) optimise pyrolysis conditions (optimal temperature treatment and residence time) for biochar production using residue obtained after faecal matter from urine diversion dry toilets was fed to black soldier fly larvae as feedstock; and (ii) determine the physicochemical and morphological characteristics of biochar produced. The residue was pyrolysed at 300, 400, and 500 C and characterised for chemical, biological and physical characteristics. Surface area (6.61 m 2 g À1), pore size, and C: N (9.28) ratio increased at 500 C for 30 min. Exchangeable bases, (Calcium) Ca, (Magnesium) Mg, (Potassium) K, and (Sodium) Na increased with increasing pyrolysis temperature. The increase in basic cations resulted in an increase in pH from 6.7 in the residue to 9.8 in biochar pyrolysed at 500 C. Biochar pyrolysed at 500 C can therefore be used to improve acidic soils. Phosphorus increased with increasing pyrolysis temperature to 3 148 mg kg À1 at 500 C. Biochar produced at 500 C for 30 min had desirable characteristics: surface area, exchangeable bases, and pH. Also, biochar can be used as a phosphorus source with potential for crop production, although an external nitrogen source is needed to meet crop nutrient requirements.

The disposal of treated wastewater from an anaerobic baffled reactor (ABR) effluent into water bodies can cause pollution. Treated wastewater management through irrigation of crops has the potential of increasing crop production through nutrient uptake while reducing the risks of environmental pollution. However, this study aimed to investigate the effect of irrigation with ABR effluent on Swiss chard yield, nutrient (N and P) uptake and leaching. Field experiments were done over three seasons at Newlands, Durban, South Africa. The experiments were laid out in a randomised complete block design with three treatments: ABR effluent irrigation (ABR), tap water irrigation with fertiliser (TWF) and rain-fed with fertiliser (RFF). Data were collected on nutrient (N and P) leaching at 30 and 50 cm depths, crop growth, soil chemical properties and nutrient uptake.Effects of irrigation with ABR effluent on soil chemical properties, Swiss chard growth, plant nutrient uptake and leaching were comparable to TWF and RFF treatments. This implies that irrigating crops with ABR effluent is a potential method for wastewater management in a manner that will not cause environmental pollution while benefiting peri-urban farmers.

No abstract

No abstract

The Decentralised Wastewater Treatment System (DEWATS) provides low cost onsite sanitation to residents living in informal settlements. Wastewater management through agriculture prevents environmental pollution and promotes sustainable agriculture. This study investigated the effects of fertigation with DEWATS effluent to field capacity in three South African soils under a banana crop. The experiment was conducted as a complete randomised design in a greenhouse with two irrigation water treatments (DEWATS effluent vs municipal tap water irrigation + fertiliser) × three soil types (Ia, Cf and Se) and four replicates over 728 days. Data were collected on crop growth, nitrogen (N) and phosphorus (P) uptake and dynamics in the soil. The DEWATS effluent significantly (p < 0.05) increased N and P uptake and soil NH+4-N and extractable P concentrations. Furthermore, DEWATS effluent fertigation significantly (p < 0.05) increased N leaching from the Ia soil and P leaching from the Cf soil. Nitrogen and phosphorus leaching from DEWATS was lower than the tap water irrigation + fertiliser treatment. There was, however, excess N and P accumulation from the DEWATS than the irrigation + fertiliser treatment, which would cause environmental concerns from runoff and leaching losses in the medium to long term.

The Decentralised Wastewater Treatment System (DEWATS) can provide a potential sanitation solution to residents living in informal settlements with the effluent produced being used on agricultural land. This paper reports on a first step to assess the technical viability of this concept. To do so a pilot DEWATS plant was connected to 83 houses in the eThekwini Municipality. An experiment was conducted in a randomised complete block design with 2 treatments (DEWATS effluent irrigation and tap water irrigation + fertiliser) and 3 blocks. Banana and taro crops were irrigated using an automated drip irrigation system. Data on the weather, crop growth, nitrogen and phosphorus uptake and soil chemical properties were collected. Irrigation with DEWATS effluent was comparable to tap water + fertiliser especially for banana growth and biomass production. Banana and taro required 3 514 mm of irrigation effluent. About 0.0117 ha·household−1 (23.3 m2·person−1) was found to be an adequate area for effluent reuse. Wet-weather storage requirements were calculated to be about 9.2 m3·household−1. DEWATS effluent, after passing through a horizontal flow wetland, was unable to meet banana and taro nitrogen and phosphorus requirements. Nutrient monitoring is required when using anaerobic filter effluent from a DEWATS for irrigating banana and taro.

The decentralised wastewater treatment system (DEWATS) is an onsite sanitation technology that can be used in areas away from municipal sewerage networks. The discharge of effluent emanating from DEWATS into water bodies may cause pollution. Agricultural use of the effluent may improve crop yields and quality thereby contributing to food security in low-income communities. There are drawbacks to the agricultural use of treated wastewater. Therefore, the study assessed the crop, environmental and health risks when irrigating with anaerobic filter (AF) effluent using the Decision Support System (DSS) of the South African Water Quality Guideline model, in four South African agroecological regions, three soil types, two irrigation systems and three different crops. The model was parameterised using AF effluent characterisation data and simulated for 45 years. The model predicted that there are no negative impacts for using AF effluent on soil quality parameters (root zone salinity, soil permeability and oxidisable carbon loading), leaf scorching and irrigation equipment. The problems were reported for nutrient loading (N and P) in maize and microbial contamination in cabbage and lettuce. It was recommended that the effluent should be diluted when used for maize production and advanced treatment should be explored to allow unrestricted agricultural use.